In fabrication of integrated circuits (ICs), it is important to test the individual circuit chip die while they are still attached in a semiconductor wafer and to test the packaged integrated circuit devices. In many testing applications, the tests must be performed over temperature. Accordingly, automated test systems are commonly outfitted with temperature control systems which can control the temperature of the wafer or device under test.
In some testing systems, such as wafer probers, the wafer is held on a temperature-controlled chuck, and electrical stimulus signals are applied to the circuits on the wafer, circuit response signals are detected via an array of electrical contact probes brought into contact with the wafer. The temperature of the chuck and, therefore, the temperature of the wafer, can be controlled by a heater and/or heat sink integrated into the chuck and by temperature-controlled fluid circulated through the chuck. Such systems are manufactured and sold by Temptronic corporation of Sharon, Mass.
In other systems, packaged ICs are tested over temperature by applying the electrical stimulus signals and receiving response signals via the IC package pins. The device under test (DUT) is held in a socket on a platform, and the test signals are routed to the pins via the socket. In one such system, the THERMOSTREAM™ system manufactured and sold by Temptronic Corporation, a temperature-controlled steam of air is directed onto the DUT to control the temperature of the DUT during testing.
As wafers become larger, and as circuits become smaller and more densely integrated, positioning tolerances for these test systems become smaller. Accordingly, it is becoming increasingly important that the support system on which the DUT or wafer is supported be mechanically stable and rigid and also extremely flat, since mechanical flaws such as distortions in the platform would adversely affect the positioning capability of the system. This is particularly important in temperature-controlled test systems, since mechanical systems tend to distort and warp over temperature. Particularly at high temperature, distortions in the support platform can become so great that substantial inaccuracies in testing can result.